An engine includes a valve (intake valve, exhaust valve) for opening and closing a region between a combustion chamber and an intake port or a region between the combustion chamber and an exhaust port. The engine is configured to control lift characteristics of the valve such as opening and closing timings and opening and closing amounts (lift amount of valve) to change its characteristics. Also, a valve operating system is proposed to change lift characteristics of the valve depending on the engine (e.g., see Japanese Laid-Open Patent Application Publication No. 2005-180232 (especially see FIGS. 1 and 2), Japanese Laid-Open Patent Application Publication No. Hei. 06-74010 (especially see FIGS. 11 and 12)).
According to the disclosure of Japanese Laid-Open Patent Application Publication No. 2005-180232, a first arm member, a pivot roller portion and a locker arm are provided between a drive cam and a valve. During rotation of the drive cam, the pivot roller portion and the first arm member rotate respectively around separate axes, and the locker arm, which is pressed by the first arm member, is pivoted around a base end portion thereof such that a tip end portion thereof moves vertically, causing the valve to reciprocate. On the other hand, when a control shaft is angularly displaced around its center axis, the attitude of the pivot roller portion with respect to the first arm member is changed, changing the lift characteristics of the valve.
According to the structure disclosed in Japanese Laid-Open Patent Application Publication No. Hei 06-74010, a pivot arm and a pivot cam are provided between a drive cam and a valve. A roller is rotatably supported in close proximity to a tip end of the pivot arm and is configured to contact the drive cam. When the drive cam rotates, a driving power is transmitted to the pivot arm and the pivot cam via the roller, and the pivot cam presses the valve, causing the valve to reciprocate.
In the structure disclosed in Japanese Laid-Open Patent Application Publication No. 2005-180232, the pivot roller portion, the first am member and others are disposed between the drive cam and the valve in addition to the locker arm and they are all pivoted during the reciprocation of the valve as described above. Therefore, an inertia moment of movable members increases. If the inertia moment increases, then it may be difficult to attain a high engine speed, or a wear amount of slidable portions may increase. Also, in the structure disclosed in patent document 2, during the rotation of the drive cam, a drive member, a pivot camshaft, a support shaft, and others are pivoted in addition to a follower and the pivot cam, increasing the inertia moment of the movable members.
The structure of Japanese Laid-Open Patent Application Publication No. Hei. 06-74010 is directed to reducing a PV value (i.e., a multiplication value of a surface pressure (P) and a sliding speed (V) at contact portions) at the time of contact between the pivot arm and the drive cam by causing the pivot arm and the drive cam to contact with the roller interposed between them. However, since the inertia moment of the movable members increases because of a weight of the roller, the maximum value of the PV value which occurs while the drive cam is rotating once can not be sufficiently reduced.
Accordingly, an object of the present invention is to provide a valve operating system which is capable of reducing an inertia moment in movable members of the valve operating system. Another object of the present invention is to provide a valve operating system which is capable of simplifying a structure for changing a phase between a driven member and a pivot cam while reducing a PV value between the drive cam and the driven member.